DC Stands for direct current, meaning that the flow of electrons in the electricity is in one circular direction. This is in contrast with AC (alternating current), which implies that the electrons flow backwards for an amount of time, then forwards again. We can clearly see the different between AC and DC on an oscilloscope-type diagaram. The top waveform is DC, where we can clearly that each oscillation is in a positive direction. The bottom is AC, with pulses in both directions.

We all know that Motors are basically Dynamo generators run in reverse. And when a dynamo generator is spun, it's output is always basic AC current. So surely, to input to an electric motor, AC is needed? Well, yes it is, however, most DC motors contain a commutator. This converts the DC input into AC before it turns the central part of the motor (this means that there is actually no such thing as a true DC motor, and in this hub "DC motor" refers to a motors which operates on a DC input.

The commutator which converts the DC into AC is usually in the form of a split ring commutator, incorporated in the motor. Originally, these used copper or carbon brushes, which would be in constant contact with the commutator ring, causing friction, which would dramatically lower the efficiency of the motor. They would also wear out after certain amounts of use and require replacement of both the brushes and the commutator ring. However, in this day and age Brushless DC Motors are common, eliminating the need for bruhes, and thus increasing both the energy and cost efficiency of running them.  

There are three main types of DC motor in production today. They are:

• Brushed DC Motors
• Brushless DC Motors
• Stepper DC Motors

For Detailed information on these motors, there working, specifications and retailers, please visit this online DC Motor Guide